Control of undesirable pyrochlore is critical to the processing of lead perovskite dielectrics and ferroelectrics. In this work, a homogeneous and stoichiometric fine powder of the ferroelectric Pb0.97La0.02(Zr0.64Sn0.25Ti0.11)O3 (PLZST) has been prepared by a hydroxide coprecipitation and freeze-drying method. Through systematic variation of processing temperature and time, we have characterized the pyrochlore-to-perovskite crystallization process of the powder. Studies of the crystallization behavior of the precursor as a function of temperature by X-ray powder diffraction and transmission electron microscopy showed that the pyrochlore phase forms from an amorphous precursor, initially at low temperatures around 500â 550â °C. Further heat treatment to 750â °C resulted in development of the perovskite phase with no significant pyrochlore crystallite growth. At intermediate temperatures the precursor yielded a fine mixture of pyrochlore and perovskite phases. When the pyrochlore phase was heat-treated in air a slight weight increase was observed in the temperature range of 300â 700â °C, which is attributed to oxygen absorption. The weight increase was not observed upon firing in argon atmosphere; instead, a weight loss occurred near 700â °C, which was identified as being mostly due to CO2 gas evolution. This implies that the pyrochlore phase is crystallographically and thermodynamically metastable. An apparent activation energy of 53.9â kcalâ mol^{â 1} was estimated for the pyrochloreâ perovskite phase transformation.